"Portrait of a High Key - is a portrait, tonal decision which determined that the dark image areas do not extend beyond the second stage of light-gray scale densities of the seven-" - "Techniques and Technology fotosemki - Feldman, Kursk

Theory of HK is here: narod.ru/disk/19968567000 /% D0% 92% D0% 9A.pdf

and : photoside.ru/blog/topic/Mifi-i-realii-Visokogo-klyucha-ili-portret-v-High-key